In some situations, we may end up calling memcg_rstat_updated() with a
value of 0, which means the stat was not actually updated. An example is
if we fail to reclaim any pages in shrink_folio_list().

Do not add the cgroup to the rstat updated tree in this case, to avoid
unnecessarily flushing it.

Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 mm/memcontrol.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 361c0bbf7283..a63ee2efa780 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -618,6 +618,9 @@ static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val)
 {
 	unsigned int x;
 
+	if (!val)
+		return;
+
 	cgroup_rstat_updated(memcg->css.cgroup, smp_processor_id());
 
 	x = __this_cpu_add_return(stats_updates, abs(val));
-- 
2.40.0.348.gf938b09366-goog

On Thu, Mar 30, 2023 at 07:18:01PM +0000, Yosry Ahmed <yosryahmed@google.com> wrote:
>  mm/memcontrol.c | 3 +++
>  1 file changed, 3 insertions(+)

Reviewed-by: Michal Koutný <mkoutny@suse.com>